Resistance isn’t futile

european regulation

By Gavin

September 7th, 2011


The ‘super’ house-mouse and the malaria carrying mosquito have made the news recently. They are just two of a growing number of pest species that are becoming less and less effected by the chemicals we use to control them. In Europe, this is quite literally a growing problem; agricultural yields are threatened by pest resistance, and regulations lack short-term solutions. The ‘super mouse’ is not a super hero, but its story may save us with the warning it carries.


One instinctive goal

We share the planet Earth with an estimated 8.7 million other species - that’s an incalculable number of individual organisms with one instinctive goal – survival.


Living organisms are not created equally; some are better equipped for survival than others. Darwin popularised the concept of ‘survival of the fittest’; a metaphor for his theory of ‘natural selection’, the more favourable chance of survival of organisms better adapted for their immediate, local environment.


Natural selection drives change in species; the genetic variations within a group of organisms may see some individuals survive in a particular environment, whilst others die out. If the advantageous genetic characteristics of the surviving organisms are passed to the next generation, then the new generation is better equipped for survival. This process can repeat until species populations have adapted themselves for particular ecological niches.


A challenge

Species adaptation represents opportunity and threat to agricultural production. Natural selection complicates the process of crop protection; pests and diseases adapt and avoid the intended effects of pesticides.


The pesticide used to treat a particular crop may not be effective on all of the target species within a target area. When this occurs, future generations of the pest are likely to share more of the genetic characteristics that protect them against the pesticide. This is known as pesticide resistance.



Pesticide resistance is not unlike the growing problem of the resistance of certain pathogens to human antibiotics. Eighty percent of the often deadly E.coli bacteria is resistant to at least one of the drugs formulated to treat it. Other non-agriculture examples that have made headlines in recent weeks, are new levels of malaria mosquito resistance to insecticides, and house-mouse resistance to rodenticides – the rise of the so called ‘super mouse’.


The Insecticide Resistance Action Committee (IRAC) defines pesticide resistance as ‘… a heritable change in the sensitivity of a pest population that is reflected in the repeated failure of a product to achieve the expected level of control …’.


Agricultural pesticide resistance has serious implications; most notably crop losses that exceed economically viable limits and, the danger of incorrect pesticide use as larger than prescribed doses may be applied in attempt to counter a lack of efficacy. Both of these scenarios pose a particular threat to the environment; in the form of over application of pesticide, or the expansion of farmland in order to compensate for crop losses.



There are a number of measures and techniques aimed at avoiding pesticide resistance (or delaying its onset), including:


  • Avoiding unnecessary pesticide applications; limiting an organism’s exposure to active ingredients delays the onset of resistance.
  • Providing refuge areas for target species; ensuring the survival of genetic susceptibility to the plant protection product.
  • Alternating between pesticide classes; rotating the use of products which have different effects on organisms lessens the probability of target species developing resistance.
  • Combining (‘tankmixing’) pesticide products in one application is another method of complicating the onset of resistance.


Avoiding the unnecessary use of pesticides and the provision of refuge areas for pest (and other) organisms, are considered good practice and relatively easy measures to implement. However, it is the efficacy and the variety of active substances available for crop protection that have the greatest bearing on resistance.


Reversing negative trends

The strength of continued product efficacy lies not only in the characteristics of an individual product, but also in the range of products formulated to treat a common threat; therefore the pesticide market should continue to offer:


  • A high standard of efficacy in all products, and
  • A suitable diversity of pesticide classes per target pest species.


Renewed European regulations continue to ensure that all crop protection products that reach the market are of high standard and are suitably effective; however, the short term effect of the 2011 implemented Directive 1107/2009 is to reduce the diversity of products on the market, this leaves European agriculture increasingly vulnerable to resistance.



Looking at the importance of the azole class of fungicides, ADAS, a UK environmental consultancy has published a report projecting their impact on wheat yields.


Triazoles (of the azole fungicide class) are the most effective defence for wheat against Septoria tritici, a fungal leaf blotch disease that presents the most significant threat to wheat crops.


The ADAS study highlights the role that innovation has played in ensuring the availability of safe and efficient crop protection products in cereal production. Triazoles were in fact developed as a defence against leaf blotch because Septoria tritici (and several other plant pathogens) developed resistance to fungicides of the strobilurin class. The study shows an estimated yield loss without triazoles of 8.7%, 6.8% and 5.0% in France, UK and Denmark respectively. The overall yield impact in Europe is initially projected to be over 7% – an amount that will increase over time as Septoria tritici develops resistance to the fewer crop protection solutions available. Losses in the region of 5-9% may be considered minor and little cause for concern; however, Losses of 50% have been reported in severely affected crops.


Europe is a leading grain producer, with wheat being the crop with by far the highest production in Europe. In 2007, wheat accounted for 46 % of cereal production in the EU. It is also one of Europe’s most widely distributed crops; in fact, only five regions do not produce wheat, namely Principado de Asturias in Spain, Valle d’Aosta/Vallée d’Aoste, Provincia Autonoma Bolzano/Bozen in Italy and Mellersta Norrland and Övre Norrland in Sweden. Wheat losses can impact the agricultural economy of almost the entire of Europe.


The ADAS report projects the triazole ban to cost the UK, France and Denmark approximately 500 million Euro per year in wheat crop losses. This is not an insignificant dent in the agricultural economy, and only considers the impact of losing one product class on one crop type in only three of the EU’s 27 wheat producing Member States.


Poor crops mean poor harvests; poor harvests mean high priced food. The cost of pesticide resistance will ultimately be paid by the consumer.


Challenge for industry, challenge for policy

Whilst the short to medium-term impacts of the loss of triazoles are a cause for concern, the challenge is clear for industry and for future European policy; innovate or suffer the economic, health and environmental problems associated with inadequate pest management.


The crop protection industry must work to develop new safe solutions to resistance, and ensure that a broad range of products are available for specific pest threats, whilst Europe needs to recognise the importance of research and development and back a regulatory framework that promotes innovation.


If we don’t invest in research and development and if politicians lose faith in science, we can expect more news of super mice, we can expect malaria to be with us for a long time to come, we can expect to suffer severe crop losses, and we can expect to be paying a lot more for our food.


One last thing

Integrated pest management (IPM) is a good practice approach to crop protection. IPM is an integrated strategy for crop management, designed to solve ecological problems when applied in agriculture. Performed in three main stages: prevention, observation, and intervention, IPM combines pesticide use with biological and sophisticated management techniques to manage pest populations in an ecological way. IPM can be used by both conventional and organic agriculture.


The use and rotation of a combination of biological and chemical protection methods means that IPM has potential to limit or delay the onset of resistance. Head over to ‘Organic, Pesticides and Integrated Pest Management’  – an earlier blog post dedicated to the subject of IPM.



  1. matthew williams

    Thursday, September 8, 2011

    Triazoles were developed after Strobilurins, not the other way round.

  2. Gavin

    Monday, September 12, 2011

    Matthew, the article does not suggest otherwise…

    “Triazoles were in fact developed as a defence against leaf blotch because Septoria tritici (and several other plant pathogens) developed resistance to fungicides of the strobilurin class.”

  3. david

    Sunday, September 23, 2012

    So when they become resistant to the old pesticide, just create another pesticide?


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